Method for producing a multi-layer paper liner web and multi-layer paper liner

Abstract

The invention relates to a method for producing a multi-layer paper liner web and a multi-layer paper liner. The method comprises forming a first web out of a first pulp and a second web out of a second pulp. The first pulp comprises water and first components other than water, wherein said first components other than water comprise 65 wt.% to 99,99 wt.% bleached virgin cellulose fibre material, and wherein as one other of the first components other than water a dye exhibiting a blackish colour is added to the first pulp. The second pulp comprises water and second component(s) other than water, wherein said second component(s) other than water comprise(s) 65 wt.% to 100 wt.% unbleached cellulose fibre material. The multi-layer paper liner comprises a top layer comprising and a support layer. The top layer comprises water and first components other than water, said first components other than water comprising 65 wt.% to 99,99 wt.% bleached virgin cellulose fibre material and a dye exhibiting a blackish colour. The support layer comprises water and second components other than water, said second component(s) other than water comprising 65 wt.% to 100 wt.% unbleached cellulose fibre material.

Description

[0001] The invention relates to a method for producing a multi-layered paper liner web, and multi-layer paper liner.

[0002] Paper-based packaging is used widely nowadays, with ever increasing amounts for various product packaging purposes. For reasons of better ecological but also economical sustainability, considerable effort is made to use paper-based packaging products wherever possible, thereby for example replacing plastic packaging or other types of packaging.

[0003] One prominent type of paper-based packaging product are so-called liners or paper liners, which can be used as stand-alone paper packaging or as part / component of a paper packaging, for example as one paper-ply in such multi-component paper packaging.

[0004] While several types of paper liners are known in the art of paper technology, the most widely used type of paper liners are multilayer products. One prominent example is a two-layer paper liner with a top layer made of good quality, virgin cellulose material which often is also bleached, and a bottom or support layer made of comparatively lower quality cellulose material, for example recycled paper and / or broke. Such layered, cellulose material combinations are for example used as top layers in paper packaging applications. Because such top layer, which in packaging applications is the layer visible to the eye, commonly comprises a high share of Kraft pulp or is basically made from Kraft pulp, such type of paper liner is also referred to or designated as Kraft liner or Kraft top. Liners facing the outside of a paper packaging product of course have particular high requirements regarding optical appearance. For many applications, the top layer of such liners is desired or required to be essentially white, having a high degree of brightness.

[0005] Regarding economic aspects, minimizing the use of virgin cellulose material or other costly ingredients / additives is desirable for production of such paper liners, in particular minimizing the use of bleached (Kraft) pulp. On the other hand, customer desires also must be considered, which customer desires typically pertain to optical appearance of a paper-based packaging, and thus to the optical appearance of paper liners above all.

[0006] Depending on the type of packaging, several criteria regarding optical appearance may have to be met. If the packaging for example is to be printed, certain surface smoothness levels may have to be fulfilled to provide for sufficient printability and print quality of a paper-based packaging comprising a paper liner to be printed for example. Other requirements on optical appearance may pertain to brightness or whiteness or specific coloration of a paper-based packaging.

[0007] One of the most prominent features related to quality of a paper packaging by customers however is uniformity of the optical appearance. A paper packaging showing highly uniform, optical appearance usually is considered as having higher quality, regardless of the actual colour of the paper itself.

[0008] Irregularities in the optical appearance of paper liners often originate from the differences in shades between the cellulose fibre materials selected for the top and support layers of typical paper or Kraft liners. Since it is desirable to use as little virgin fibre material as possible for the top layer / ply, said top layers are sought to be produced as thin as possible. This however causes the bottom or support layer being made of lower quality cellulose material to at least partially shine through the top layer, thereby causing a stained optical appearance of the liner due to the mentioned different shades of the cellulose materials. Such ununiform, optical appearance commonly is referred to as mottling in paper making technology.

[0009] In the prior art several ways to impede or reduce mottling of multi-ply paper liners are known. The most obvious and most commonly used method is to increase the grammage of the top ply or layer to a level, that the bottom or support layer does not shine through enough to actually cause mottling. Other ways include the addition of layers / plies for better optical coverage of the support ply, coatings on the top layer or addition of substances for covering the bottom / support ply and impeding shining through of said support layer comprising lower quality cellulose fibre material. All these measures however involve a higher usage of costly materials, therefore foiling the desires to reduce the use of such materials.

[0010] An objective of the invention was to address the deficiencies still existing in the prior art and to provide an improved method for producing a multi-layer paper liner web with reduced mottling in a more ecologic and economic sustainable way. Another objective of the invention was to provide a multi-layer paper liner with reduced mottling, which can be produced in an improved, more ecologic and economic sustainable way.

[0011] One objective is achieved by providing a method as specified in the corresponding claims.

[0012] The method for producing a multi-layer paper liner web, in particular a multi-layer paper liner web with at least a first paper web layer with a white surface, comprises providing a first pulp consisting of 95 wt.% to 99,9 wt.% water and 0,1 wt.% to 5 wt.% first components other than water, said first components other than water comprising 65 wt.% to 99,99 wt.% bleached virgin cellulose fibre material, based on 100 wt.% total weight of all first components other than water, providing a second pulp consisting of 95 wt.% to 99,9 wt.% water and 0,1 wt.% to 5 wt.% second component(s) other than water, said second component(s) other than water comprising 65 wt.% to 100 wt.% unbleached cellulose fibre material, based on 100 wt.% total weight of all second component(s) other than water, forming a first web out of the first pulp and forming a second web out of the second pulp, joining the first web and the second web to one another, thereby forming a multi-layer web with the first web constituting a first paper web layer and the second web constituting a second paper web layer, wherein the first web and the second web are connected to each other, dewatering and drying the first web and the second web in multiple dewatering / drying steps to form the multi-layer paper liner web having a first paper web layer formed from the dewatered / dried first web and a second paper web layer formed from the dewatered / dried second web, the first paper web layer and the second paper web layer being connected with each other.

[0013] As one of the first components other than water of the first pulp a dye exhibiting a blackish colour is added to the first pulp.

[0014] The method hereby comprises all the steps listed above. However, the sequence of method steps listed above and in claim 1 does not need to be executed strictly in the order as provided above and in claim 1. As long as it makes sense in technical regard, the sequence of the individual process steps listed above and in claim 1 can be swapped or carried out in an interchanging manner. For example, it may be convenient to apply the method step of dewatering and drying the first and second paper webs at least partially, i.e. to a certain degree of dryness or to a certain water content, before carrying out the method step of joining the first and second webs to one another. It may however also be convenient to form the multi-layer web by joining the first and the second webs with basically the initial water contents of the first and second pulps without significant dewatering before the method step of joining the first and second webs and forming the multi-layer web. Furthermore, the first web and second web may be dewatered and dried at least almost fully to a desired water content, and then joined to one another without subsequent drying. In the latter case, a binder may for example be used for the joining. In other words, the first web and the second web may be dewatered / dried in the multiple drying steps either separately from one another or in the already joined state at any stage within the method, wherein the step of joining the first and second webs can be carried out before dewatering / drying of the first and second webs is commenced, after dewatering / drying of the first and second webs is completed, or after the first and second webs are partially dewatered / dried with further drying after the joining.

[0015] As already mentioned, the optical appearance of liners for many liner applications is required to be essentially white, with high brightness. Therefore, an actual removal of colour is desirable for such applications, and that is why processes such as bleaching are often used for production of such white top Kraft liners, to remove or lighten colour and to whiten materials of the liners. However, the inventors surprisingly found that a dye exhibiting a blackish colour is very effective in reducing mottling of a multi-layer paper or paper web. The term black dye may be used instead of the term dye exhibiting a blackish colour. In other words, the dye exhibiting a blackish colour may be a black dye.

[0016] In principle, any dye exhibiting a blackish colour suitable for paper making can be used. In a preferred embodiment, a water-soluble dye exhibiting a blackish colour may be added to the first pulp. Such water-soluble dyes are also referred to as direct dyes. In particular, an anionic, water-soluble direct dye exhibiting a blackish colour may be added to the first pulp. As one example for a suitable dye exhibiting a blackish colour, the product sold under the name Pergasol ™< Black 18 Lna by Solenis ™< can be mentioned.

[0017] Surprisingly, the mottling reduction efficiency of dyes exhibiting a blackish colour was found to be vastly superior to that of other types of dyes. Merely a low amount of dye exhibiting a blackish colour is necessary for effective mottling reduction, such that the addition of the black dye also does not lead to undesired colouring effects. In particular, changes in colour or brightness are barely visible to the naked eye, such that the first paper web layer may still have a white surface. For example, the first paper web layer may have a brightness according to ISO 2470 of at least 65%, preferably at least 70 %. Some examples showing the remarkably efficient mottling reduction by way of adding the dye exhibiting a blackish colour are given beneath.

[0018] Overall, the addition of the dye exhibiting a blackish colour allows for a cost-efficient and sustainable production of multi-layer paper liner webs and paper liners with improved visual appearance and printability, as the reduction of mottling can be achieved without the need for higher amounts of bleached virgin fibres, additional covering layers or coatings and / or other more costly measures.

[0019] In one embodiment of the method, the dye exhibiting a blackish colour may be added to the first pulp in an amount of 0,01 wt.% to 0,1 wt.% based on 100 % total weight of all first components other than water.

[0020] The inventors found that the dye exhibiting a blackish colour is very effective in reducing mottling of a multi-layer paper liner or paper liner web, even when added in the very low amounts to the first paper web layer, as specified above. Therefore, high quality multi-layer paper liner webs with a white first paper web layer showing high brightness may be produced be means of the method, with very little effort necessary for effective mottling reduction. Preferably, the dye exhibiting a blackish colour can be added to the first pulp in an amount of 0,012 wt.% to 0,05 wt.% based on 100 % total weight of all first components other than water.

[0021] In another embodiment of the method, a recycled wastepaper material may be used as unbleached cellulose fibre material of the second pulp.

[0022] In this regard, the method allows for using high amounts of recycled wastepaper material, since mottling can effectively be impeded by means of the method. Thereby, making use of recycled wastepaper further helps reducing costs.

[0023] In particular, a recycled wastepaper material selected from a group consisting of wastepaper types according to EN 643 with the designation 1.02, 1.04, 1.05 and 4.01, or a mixture of said wastepaper types may be used as unbleached cellulose fibre material of the second pulp. These types of wastepaper have proven to be cost-effective and readily available raw materials. On the other hand, those wastepaper types nevertheless allow for the production of paper liner webs and paper liners with good mechanical strength, while at the same time low energy and water input is needed for the stock or pulp preparation.

[0024] In another embodiment of the method a cellulose fibre material consisting of 30 wt.% to 70 wt.% recycled long fibre material, 20 wt.% to 60 wt.% recycled short fibre material and 10 wt.% to 50 wt.% broke may be used as unbleached cellulose fibre material of the second pulp.

[0025] A corresponding composition of the unbleached cellulose fibre material of the second pulp bears the advantage that a paper liner web with good mechanical properties, in particular with high tensile strength can be produced.

[0026] In a preferred embodiment of the method, it may be convenient to set a consistency of both the first web and the second web to 8 % to 14 % respectively immediately before joining the first web and the second web to one another and forming the multi-layer web.

[0027] Consistencies immediately before the paper layers are connected may also be referred to as combining consistencies. As it turned out, the first and second webs can be joined / connected particularly well within the specified dry contents or consistencies range. As a result, very good adhesion of the webs to one another, and thus a multi-layer web with strongly joined webs can be provided. In particular, delamination of the first and second web can effectively be impeded. Moreover, within the specified consistencies a transfer of substances or contaminants from one web to the other web can be impeded.

[0028] It may also be beneficial within the method to add an optical brightening agent to the first pulp as another first component other than water of the first pulp, in an amount of 0,03 wt.% to 0,5 wt.%, based on 100 % total weight of all first components other than water.

[0029] In general, the brightness of the paper liner web as viewed from the side of first paper web layer may be adjusted by adding the optical brightening agent. The addition of such optical brightening agent within the range for amounts given thereby allows for setting the brightness to any brightness value common for paper liners and paper liner webs. Optical brightening agents of the Tetrasulfo or Disulfo classes can be mentioned as examples for suitable optical brightening agents.

[0030] Another embodiment of the method may comprise, that as another first component other than water of the fist pulp, precipitated and / or ground calcium carbonate is added to the first pulp in an amount of 10 wt.% to 25 wt.%, based on 100 % total weight of all first components other than water.

[0031] On the one hand, the addition of precipitated and / or ground calcium carbonate enables a more cost-efficient and sustainable production of the paper liner web in general, as the more costly and ecologically unsustainable cellulose material, especially bleached virgin fibre material, can at least partially be replaced by the precipitated and / or ground calcium carbonate. On the other hand, the inventors also presume that the precipitated and / or ground calcium carbonate may assist in distributing the dye exhibiting a blackish colour in particular during forming of the first web, thereby leading to a more homogenous distribution of the dye exhibiting a blackish colour in the first paper web layer and further enhancing the mottling reduction efficiency exhibited by such black dye.

[0032] It may also be convenient in yet another embodiment of the method to add precipitated and / or ground calcium carbonate as another second component other than water to the second pulp, in an amount of 15 wt.% to 35 wt.%, based on 100 % total weight of all second components other than water.

[0033] Such addition of precipitated or ground calcium carbonate, or a mixture of both to the second pulp also allows for a more sustainable and cost-efficient production of the paper liner web.

[0034] In yet another embodiment of the method, a grammage of the first paper web layer of the multi-layer paper liner web after complete dewatering / drying may be set to 45 g / m 2< to 63 g / m2.

[0035] The inventors found, that in combination with the addition the dye exhibiting a blackish colour, a grammage of the first paper web layer within the given range is sufficiently covering the second paper web layer, thus providing sufficient mottling reduction. On the other hand, keeping the grammage of the first paper web layer within the noted range allows for a more sustainable and cost-efficient production of the multi-layer paper web as compared to the prior art, since high amounts of bleached, virgin cellulose fibre material can be avoided. Preferably, a grammage of the first paper web layer of the multi-layer paper liner web after complete dewatering / drying may be set to 45 g / m 2< to 61 g / m 2< , even more preferably to 45 g / m 2< to 57 g / m 2< .

[0036] Another objective of the invention is achieved by providing a multi-layer paper liner as specified in the corresponding claims.

[0037] The multi-layer paper liner can be produced by a method as specified above, wherein the method may or may not comprise any of the embodiments described in conjunction therewith above. The multi-layer paper liner can be a cut paper liner web produced by the method in this regard.

[0038] The multi-layer paper liner, in particular multi-layer paper liner with at least a top layer with a white surface, comprises a top layer consisting of 6 wt.% to 11 wt.% water and 89 wt.% to 94 wt.% first components other than water, said first components other than water comprising 65 wt.% to 99,99 wt.% bleached virgin cellulose fibre material, based on 100 wt.% total weight of all first components other than water, a support layer consisting of 6 wt.% to 11 wt.% water and 89 wt.% to 94 wt.% second components other than water, said second component(s) other than water comprising 65 wt.% to 100 wt.% unbleached cellulose fibre material, based on 100 wt.% total weight of all second components other than water, wherein the top layer and the support layer are connected to each other.

[0039] The top layer comprises a dye exhibiting a blackish colour as one of the first components other than water.

[0040] The inventors surprisingly found that the dye exhibiting a blackish colour is very effective in reducing mottling of the multi-layer paper liner. The term black dye may be used instead of the term dye exhibiting a blackish colour. In other words, the dye exhibiting a blackish colour may be a black dye.

[0041] In principle, any dye exhibiting a blackish colour suitable for paper making can be present in the top layer. In a preferred embodiment, the top layer may comprise a water-soluble dye exhibiting a blackish colour. Such water-soluble dyes are also referred to as direct dyes. In particular, the top layer may comprise an anionic, water-soluble direct dye exhibiting a blackish colour. As one example for a suitable dye exhibiting a blackish colour the product sold under the name Pergasol ™< Black 18 Lna by Solenis ™< can be mentioned.

[0042] Surprisingly, the mottling reduction efficiency of dyes exhibiting a blackish colour was found by the inventors to be vastly superior to that of other types of dyes. Merely a low amount of a dye exhibiting a blackish colour is necessary for effective mottling reduction, so that such black dye also does not lead to undesired colouring effects. In particular, changes in colour or brightness due to the dye exhibiting a blackish colour in the top layer are barely visible to the naked eye, so that the top layer may have a white surface. For example, the top layer may have a brightness according to ISO 2470 of at least 65%, preferably at least 70 %. Some examples showing the remarkably efficient mottling reduction by the dye exhibiting a blackish colour are given beneath.

[0043] Overall, the presence of the dye exhibiting a blackish colour in the top layer allows for a cost-efficient and sustainable production of the multi-layer paper liner with improved visual appearance and printability, as the reduction of mottling can be achieved without the need for high amounts of bleached virgin fibres, additional covering layers or coatings and / or other more costly measures.

[0044] If produced according to the method described above, the first paper web layer of the initially produced multi-layer paper liner web may constitute the top layer of the multi-layer paper liner, and the second paper web layer of the initially produced multi-layer paper liner web may constitute the support layer of the multi-layer paper liner, upon cutting the multi-layer paper liner web to multi-layer paper liners of a respective desired size and shape.

[0045] In an embodiment of the multi-layer paper liner, the top layer may comprise 0,01 wt.% to 0,1 wt.% of the dye exhibiting a blackish colour, based on 100 % total weight of all first components other than water.

[0046] The inventors found that the dye exhibiting a blackish colour is very effective in reducing mottling of a multi-layer paper liner, even when present in the top layer in the very low amounts specified above. Therefore, high quality multi-layer paper liners with a white top layer showing high brightness may be provided with improved mottling reduction. Preferably, the top layer may comprise 0,012 wt.% to 0,05 wt.% of the dye exhibiting a blackish colour as one of the first components other than water, based on 100 % total weight of all first components other than water.

[0047] Another embodiment of the multi-layer paper liner may provide, that the unbleached cellulose fibre material of the support layer is a recycled wastepaper material.

[0048] Due to the mottling reduction, recycled wastepaper material poses no particular problems, wherein the production costs of the multi-layer paper liner may further be reduced in this way.

[0049] In particular, the unbleached cellulose fibre material may be a recycled wastepaper material selected from a group consisting of wastepaper types according to EN 643 with the designation 1.02, 1.04, 1.05 and 4.01, or a mixture of said wastepaper types.

[0050] These types of wastepaper have proven to be cost-effective and readily available raw materials, but these wastepaper types also provide for multi-layer paper liners with good mechanical strength when present in the support layer.

[0051] In another embodiment of the multi-layer paper liner, the unbleached cellulose fibre material of the support layer may consist of 30 wt.% to 70 wt.% recycled long fibre material, 20 wt.% to 60 wt.% recycled short fibre material and 10 wt.% to 50 wt.% broke.

[0052] Such composition of the unbleached cellulose fibre material of the support layer also brings about good mechanical properties of the multi-layer paper liner, in particular high tensile strength.

[0053] It may also be advantageous, when the top layer comprises 0,03 wt.% to 0,5 wt.% optical brightening agent as another first component other than water of the top layer, based on 100 % total weight of all first components other than water.

[0054] By way of this measure, a brightness of the multi-layer paper liner as viewed from the side of the top layer can be adjusted as desired. An optical brightening agent present in the above noted range thereby allows for adjustment of the brightness of the top layer to a value common for multi-layer paper liners. As examples for suitable optical brightening agents the Tetrasulfo or Disulfo classes of optical brightening agents can be mentioned.

[0055] In another embodiment of the multi-layer paper liner, the top layer may comprise 10 wt.% to 25 wt.% precipitated and / or ground calcium carbonate as another first component other than water of the top layer, based on 100 % total weight of all second components other than water.

[0056] By means of this feature, the multi-layer paper liner can be produced in a more cost-efficient and sustainable way, since the more costly and unsustainable cellulose material, especially bleached virgin fibre material, can at least partially be replaced by the precipitated and / or ground calcium carbonate. Furthermore, the precipitated and / or ground calcium carbonate may provide for a better homogenous distribution of the dye exhibiting a blackish colour within the top layer, wherein it is believed that the precipitated and / or ground calcium carbonate assists in distributing the black dye in particular during web forming. Overall, the precipitated and / or ground calcium carbonate in conjunction with the dye exhibiting a blackish colour appears to enhance mottling reduction even further.

[0057] In yet another embodiment, the support layer may comprise 15 wt.% to 35 wt.% precipitated and / or ground calcium carbonate as another second component other than water of the support layer, based on 100 % total weight of all second components other than water.

[0058] This measure also allows for production of the multi-layer paper liner in a more sustainable and cost-efficient way.

[0059] The top layer of the multi-layer paper liner may have a grammage of 45 g / m 2< to 63 g / m 2< .

[0060] The inventors found, that in combination with the dye exhibiting a blackish colour, a grammage of the top layer within the given range is sufficiently covering the support layer, thus providing sufficient mottling reduction. On the other hand, a grammage of the first paper web layer within the noted range allows for a more sustainable and cost-efficient production of the multi-layer paper liner as compared to the prior art, since high amounts of bleached, virgin cellulose fibre material can be avoided. Preferably, a grammage of the top layer of the multi-layer paper liner may be 45 g / m 2< to 61 g / m 2< , in particular 45 g / m 2< to 57 g / m 2< .

[0061] To provide a better understanding, the invention is described in more detail in the following based on exemplary embodiments shown in the figures. These are merely preferred, exemplary embodiments however, and those having ordinary skill in the art will appreciate that the invention also can be carried out in technical meaningful ways deviating from these exemplary embodiments. Such technical possible deviations from the exemplary embodiments lie within the reach of a person skilled in the technical field of paper making, and various modifications of the exemplary embodiments can be chosen and executed by such person of ordinary skill in the art to meet actual requirements for the paper liner web to be produced, such as application and / or quality requirements for example.

[0062] The figures each show highly simplified, schematic drawings illustrating the following: Fig. 1An exemplary embodiment showing possible method steps stock preparation pulp preparation of a first pulp and a second pulp in a stock preparation unit; Fig. 2An exemplary embodiment showing possible method steps for producing a multi-layer paper liner web out of the first pulp and the second pulp; Fig. 3An exemplary embodiment showing a multi-layer paper liner.

[0063] Introductory, it should be pointed out, that the same parts described in the different embodiments are denoted by the same reference numbers and the same component names and the disclosures made throughout the description can be transposed in terms of meaning to same parts bearing the same reference numbers or same component names. Furthermore, the positions chosen for the purposes of the description, such as top, bottom, side, etc., relate to the drawing specifically being described and can be transposed in terms of meaning to a new position when another position is being described.

[0064] The product of the method is a multi-layer paper liner web, in particular a multi-layer paper liner web with at least a first paper web layer with a white surface, which subsequently can be cut into ready to use multi-layer paper liners by conventional means known in the art. Since the product produced by the method is a multi-layer web, the method comprises providing a first pulp and a second pulp for preparing at least two layers of the multi-layer paper liner web, and the subsequent processing of the two pulps. The preparation of the pulps and their subsequent processing to produce the multi-layer paper liner web can in principle be executed by any methods known in the art for the production of multi-layer webs, employing parameters usual and common in paper making technology.

[0065] In Fig. 1 an exemplary embodiment for providing or preparing the first pulp 1 and the second pulp 2 is shown. Fig.1 schematically shows a stock preparation unit 3 for preparing the first pulp 1 and the second pulp 2.

[0066] The first pulp 1 is provided consisting of 95 wt.% to 99,9 wt.% water and 0,1 wt.% to 5 wt.% first components other than water, said first components other than water comprising 65 wt.% to 99,99 wt.% bleached virgin cellulose fibre material, based on 100 wt.% total weight of all first components other than water.

[0067] For providing or preparing the first pulp 1, the bleached virgin cellulose fibre material 4 can for example be fed into a first pulp preparation line 5 with a desired water content, and can optionally be processed on the input side of the first pulp preparation line 5 by grinding / refining. For this purpose, a refiner 6 may be used for example to set a desired Schopper-Riegler value for the bleached virgin cellulose fibre material 4. Depending on the individual, specific requirements and the input quality of the bleached virgin cellulose fibre material, such grinding or refining may however also be omitted.

[0068] For preparation of the first pulp 1, a first stock flow comprising the bleached virgin cellulose fibre material 4 can be fed into a first mixing chest 7, wherein one or more additive(s) 8, such as for example sizing agents, starch or other bulk additives known in the art of paper making, may be added and admixed as further first components other than water to the first stock flow. Such additives 8 may also include further pigments or dyes, for example for colouration purposes, respectively for production of coloured multi-layer paper liner webs 30.

[0069] Preferably as another first component other than water of the first pulp, an optical brightening agent may be added to the first pulp in an amount of 0,03 wt.% to 0,5 wt.%, based on 100 % total weight of all first components other than water. Optical brightening agents of the Tetrasulfo or Disulfo classes can be mentioned as examples for suitable optical brightening agents.

[0070] Alternatively, or in addition, as another first component other than water of the fist pulp, precipitated and / or ground calcium carbonate may be added to the first pulp in an amount of 10 wt.% to 25 wt.%, based on 100 % total weight of all first components other than water. Either such optical brightening agent or precipitated and / or ground calcium carbonate, or all of them, may be added to the first stock flow, and thus to the first pulp 1 as additives 8 by feeding into the first mixing chest 7 shown in Fig. 1. Alternatively, these additives 8 may also be added at another stage of preparing the first pulp 1. In other embodiments however, such additives 8 may not be used at all, or other additives 8 as mentioned in conjunction with the embodiment disclosed with reference to the figures may be used alternatively or in addition.

[0071] The first stock flow may then for example be further homogenized in a first machine chest 9, as is commonly known in the art. Subsequently, the homogenized, first stock flow may be fed into a first dilution and cleaning unit 10, wherein the first stock flow may be diluted with water 11 to set a desired water content or consistency for the first pulp 1.

[0072] As one of the first components other than water of the first pulp a dye 12 exhibiting a blackish colour is added to the first pulp 1. Preferably the dye 12 exhibiting a blackish colour may be added to the first pulp 1 in an amount of 0,01 wt.% to 0,1 wt.% based on 100 % total weight of all first components other than water. In particular, the dye 12 exhibiting a blackish colour may be added to the first pulp 1 in an amount of 0,012 wt.% to 0,05 wt.% based on 100 % total weight of all first components other than water. The term black dye may be used instead of the term dye exhibiting a blackish colour. In other words, the dye exhibiting a blackish colour may be a black dye.

[0073] In principle, any dye 12 exhibiting a blackish colour suitable for paper making can be used. In a preferred embodiment, a water-soluble dye 12 exhibiting a blackish colour may be added to the first pulp 1. Such water-soluble dyes 12 are also referred to as direct dyes 12. In particular, an anionic, water-soluble direct dye 12 exhibiting a blackish colour may be added to the first pulp 1. The product sold under the name Pergasol ™< Black 18 Lna by Solenis ™< can be mentioned as one example for a suitable dye exhibiting a blackish colour.

[0074] In the exemplary embodiment shown in Fig. 1, the dye 12 exhibiting a blackish colour is shown to be added after the first stock solution has passed the first machine chest 9, respectively in course of the diluting and cleaning of the first stock flow in the first dilution and cleaning unit 10. The dye 12 exhibiting a blackish colour or black dye 12 may however also be added at another stage of the first pulp preparation line 5, for example together with other additive(s) 8 added to the first stock flow in the first mixing chest 7. After the final setting of the water content / consistency, the first pulp 1 can be fed to a first headbox 13 to be fed into a paper machine 14 for forming a web and further processing.

[0075] In parallel to providing the first pulp 1, the second pulp 2 is also be provided / prepared using a second pulp preparation line 15, as shown in Fig. 1. The second pulp 2 is thereby provided consisting of 95 wt.% to 99,9 wt.% water and 0,1 wt.% to 5 wt.% second component(s) other than water, said second component(s) other than water comprising 65 wt.% to 100 wt.% unbleached cellulose fibre material, based on 100 wt.% total weight of all other second components other than water.

[0076] As unbleached cellulose fibre material a recycled wastepaper material may be used. Preferably, a recycled wastepaper material selected from a group consisting of wastepaper types according to EN 643 with the designation 1.02, 1.04, 1.05 and 4.01, or a mixture of said wastepaper types may be used as unbleached cellulose fibre material.

[0077] In particular, a cellulose fibre material consisting of 30 wt.% to 70 wt.% recycled long fibre material 15, 20 wt.% to 60 wt.% recycled short fibre material 17 and 10 wt.% to 50 wt.% broke may be used as unbleached cellulose fibre material.

[0078] In the embodiment shown in Fig. 1, recycled long fibre material 16 of the unbleached cellulose fibre material for example may first be processed in a processing device 17 for removing contaminants, in particular particulate contaminants, which are often present in recycled long fibre material 16. According to the exemplary embodiment of Fig. 1, processed, recycled long fibre material 16 may than be combined with recycled short fibre material 18 and fed into a second mixing chest 19 of the second pulp preparation line 15. At this stage, broke 20 may also be added / fed into the second mixing chest 19.

[0079] As in case of the first mixing chest 7 of the first pulp preparation line 5, one or more additive(s) 21 known in the art of paper making may also be added and admixed as further second components other than water. In particular, precipitated and / or ground calcium carbonate may be added into the second mixing chest 19, and thus to the second pulp 2, as another second component other than water of the second pulp 2, in an amount of 15 wt.% to 35 wt.%, based on 100 % total weight of all second components other than water.

[0080] A second stock flow with all the above mentioned components added / mixed may than be fed from the second mixing chest 19 to a second machine chest 22 for further homogenization. After homogenization, the second stock flow may than be fed to a second dilution and cleaning unit 23as shown in the example of Fig. 1. Within the second dilution and cleaning unit 23, the stock flow can be diluted with water 11 to a desired consistency or water content and be cleaned to form the second pulp 2. According to the exemplary embodiment shown in Fig.1, the second pulp 2 may then be fed to a second headbox for injection into the paper machine 14.

[0081] In Fig. 2 an exemplary embodiment of a paper machine 14 or paper machine 14 configuration for carrying out the method is shown to illustrate the method. As has already been mentioned, the embodiment of the method shown in Fig. 2 (as well as Fig.1) is only exemplary however, and other paper machine 14 configuration may be used by those of ordinary skill in the art for carrying out the method, depending on the type of paper web liner to be produced and other requirements.

[0082] In any case, the method comprises a step of forming a first web 25 out of the first pulp 1 and forming a second web 26 out of the second pulp 2. The method further comprises a step of joining the first web 25 and the second web 26 to one another, thereby forming a multi-layer web 27 with the first web 25 constituting a first layer 28 and the second web 26 constituting a second layer 29, wherein the first web 25 and the second web 26 are connected to each other. The method in all cases also comprises a multiple-step dewatering and drying of the first web 25 and the second web 26 in multiple dewatering / drying steps to form the multi-layer paper liner web 30 having a first paper web layer 31 formed from the dewatered / dried first web 25 and a second paper web layer 32 formed from the dewatered / dried second web 26, the first paper web layer 31 and the second paper web layer 32 being connected with each other.

[0083] In the embodiment illustrated in Fig. 2, the first web 25 and the second web 26 are formed in a forming section 33 of the paper machine 14. In this exemplary embodiment a so-called hybrid former 34 may for example be used to form the first web 25, and a so-called gap former 35 may be used to form the second web 26 in parallel. In the embodiment shown in Fig. 2, both the first web 25 and the second web 26 may thus be formed and also be dewatered in a first dewatering / drying step within the forming section 33 of the paper machine 14 configuration to a desired water content or consistency. The initial dewatering of the webs 25, 26 may be conducted by means of wire meshes and suction means of the hybrid former 34 and gap former 35 respectively, thus by means commonly known in the art. In the example illustrated in Fig. 2, the first web 25 and the second web 26 having been dewatered to a desired water content are then joined at the end of the forming section 33. Preferably, a consistency of both the first web 25 and the second web 26 may be set to 8 % to 14 % respectively, more preferably to 10% to 12%, immediately before joining the first web 25 and the second web 26 to one another and forming the multi-layer web 27.

[0084] In particular regarding the steps of joining the first web 25 and the second web 26 and the multi-step dewatering / drying of the first web 25 and the second web 26, the method may well be carried out deviating from the example illustrated in Fig.2. In an alternative, not shown embodiment of the method, both the first pulp 1 and the second pulp 2 may for example be fed to one single headbox for forming the first web 25 and the second web 26. In such case a so-called multi-ply or multi-layer headbox may be used for forming the webs 25, 26 out of the pulps 1, 2, wherein the such formed webs 25, 26 may be joined immediately after web formation without significant dewatering of the webs 25, 26.

[0085] In another, not shown embodiment of the method deviating from the example shown in Fig. 2, the first web 25 and the second web 26 may be dewatered and dried almost fully to a desired, final water content, and then joined to one another without subsequent drying. In principle, the first web 25 and the second web 26 may be dewatered / dried in the multiple drying steps separately from one another and / or in the already joined state at any stage within the method, wherein the step of joining the first and second webs 25, 26 can be carried out before dewatering / drying of the first and second webs 25, 26 is commenced, after dewatering / drying of the first and second webs 25, 26 is completed, or after the first and second webs 25, 26 are partially dewatered / dried with further drying after the joining.

[0086] Referring again to the exemplary embodiment illustrated in Fig. 2, the multi-layer web 27 comprising the first web 25 and the second web 26, may after joining the webs 25, 26 be processed in a further one of the multiple dewatering / drying steps by means of a press section 36. In the example given in Fig. 2, the multi-layer web 27 may for example be processed and dried by means of a press section 36 comprising a so-called TriNip press 37, which is commonly known in the art. The multilayer web 27 may for example be dewatered / dried to a consistency of about 45 % to 54 % by means of the press section 36.

[0087] Having a water content within this range, the multi-layer web 27 respectively the joined first and second webs 25, 26 may then be for example subjected to surface treatment by means of a surface processing unit 38 as illustrated by the example depicted in Fig. 2. Typically, such surface treatment may involve an application of one or more surface treatment substance(s) to the surface of the first web 25 respectively the first layer 28, and / or the second web 26 respectively the second layer 29. Common substances / chemicals applied to the surface(s) of the multi-layer web 27 include resins, glues or starch. Since these substances are often referred to as sizing agents, such surface treatment unit 38 often is denoted as size press in paper making technology. Alternatively to the embodiment shown in Fig. 1, such surface treatment of the multi-layer web 27 may also be carried out elsewhere in the paper machine 14, for example after the multi-layer web 27 has partially or completely passed the dryer section 40 described next, or surface treatment may be omitted completely.

[0088] The final drying step In paper making is commonly carried out by means of a dryer section 40, wherein such dryer section may be configured as two-part dryer section 40 having a pre-drying section 41 and a post-drying section 42 as illustrated in Fig. 2. Between such pre-drying section 41 and post-drying section 42, a surface treatment unit 38 may be arranged for surface treatment of the multi-layer web 27. Independent thereof, the dryer section 40 may comprise a variety of cylinders 43, which may be steam-heated cylinders as is commonly known. The multi-layer web 27 may be dried by means of such dryer section 40 as last drying step, to form the multi-layer paper liner web 30 with a first paper web layer 31 formed from the dewatered / dried first web 25 and the second paper web layer 32 formed from the dewatered / dried second web 26, as illustrated in Fig. 2.

[0089] A grammage of the first paper web layer 31 of the multi-layer paper liner web 30 comprising the more expensive materials, may be set to 45 g / m 2< to 63 g / m 2< , and preferably be set to 45 g / m 2< to 61 g / m 2< , and even more preferably to 45 g / m 2< to 57 g / m 2< , after complete dewatering / drying is completed. In general, the first paper web layer 31 may have a brightness according to ISO 2470 of at least 65%, preferably at least 70 %.

[0090] Typically, the multi-layer paper liner web 30 may be wound up onto a carrier-roll 44 after finishing, for example for transport to an intended application location. For finishing, the multi-layer paper liner web 30 may be subjected to an additional surface treatment prior to winding up or otherwise assembling. For example, the multi-layer paper liner web 30 may be processed by means of a calender 45 to smoothen the surfaces of the of the multi-layer paper liner web 30 as illustrated in Fig. 2.

[0091] As another possible alternative to the exemplary embodiments shown in Fig. 1 and Fig. 2, it should be mentioned, that the arrangement of the first pulp preparation line 5 and second pulp preparation line 15, and thus also the arrangement of the headboxes 13, 24 and hybrid former 34 and gap former 35 may be swapped, such that the multi-layer web 27 is transported through the various stages of the paper machine 14 with the first layer 28 and the second layer 29 also being swapped, or upside-down respectively as compared with or in contrast to the embodiments shown in Fig. 1 and Fig. 2.

[0092] In addition to the exemplary embodiment shown in Fig. 1 and Fig. 2, the multi-layer paper liner web 30 may be produced comprising one or more additional paper layers attached to the second paper web layer 32.

[0093] The multi-layer paper liner web 30 may be cut to multi-layer paper liners 45 for further use, for example as component of a packaging product or as stand-alone packaging product, which cutting typically is done at the production or application location.

[0094] An exemplary embodiment of such multi-layer paper liner 45 cut from a multi-layer paper liner web 30 is shown in Fig. 3.

[0095] As can be depicted from Fig. 3, the multi-layer paper liner 45 comprises a top layer 46 and a support layer 47, wherein one or more additional layers 48 may optionally be attached or joined to the support layer 47. The top layer 46 may thus be formed by dewatering / drying the first web 25 of the multi-layer web 27 of the above-described method to form the first paper web layer 31 of the multilayer paper liner web 30, and the support layer 47 may be formed by dewatering / drying the first web 25 of the multi-layer web 27 to form the second paper web layer 32 of the multilayer paper liner web 30, with subsequent cutting of the multilayer paper liner web 30. In particular, the top layer 46 of the multi-layer paper liner 45 may have a white surface. For example, the top layer 46 may have a brightness according to ISO 2470 of at least 65%, preferably at least 70 %.

[0096] The top layer 46 of the multi-layer paper liner 45 consists of 6 wt. % to 11 wt.% water and 89 wt. % to 94 wt.% first components other than water, said first components other than water comprising 65 wt.% to 99,99 wt.% bleached virgin cellulose fibre material, based on 100 wt. % total weight of all first components other than water. The support layer 47 consists of 6 wt. % to 11 wt.% water and 89 wt. % to 94 wt.% second components other than water, said second component(s) other than water comprising 65 wt.% to 100 wt.% unbleached cellulose fibre material, based on 100 wt. % total weight of all first components other than water. As can be seen from Fig. 3, the top layer 46 and the support layer 47 of the multi-layer paper liner 45 are connected to / with each other.

[0097] The top layer 46 comprises a dye exhibiting a blackish colour as one of the first components other than water. Preferably, the top layer 46 may comprise 0,01 wt.% to 0,1 wt.% of the dye exhibiting a blackish colour, in particular may comprise 0,012 wt.% to 0,05 wt.% of the dye exhibiting a blackish colour, based on 100 % total weight of all first components other than water. The term black dye may be used instead of the term dye exhibiting a blackish colour. In other words, the dye exhibiting a blackish colour may be a black dye.

[0098] In principle, any black dye suitable for paper making can be present in the top layer 46. In a preferred embodiment, the top layer 46 may comprise a water-soluble dye exhibiting a blackish colour. Such water-soluble dyes are also referred to as direct dyes. In particular, the top layer 46 may comprise an anionic, water-soluble direct dye exhibiting a blackish colour. The product sold under the name Pergasol ™< Black 18 Lna by Solenis ™< is an example for a suitable dye exhibiting a blackish colour.

[0099] The unbleached cellulose fibre material of the support layer 47 may be a recycled wastepaper material. In particular, the unbleached cellulose fibre material of the support layer 47 may be a recycled wastepaper material selected from a group consisting of wastepaper types according to EN 643 with the designation 1.02, 1.04, 1.05 and 4.01, or a mixture of said wastepaper types.

[0100] Independent of this, the unbleached cellulose fibre material of the support layer 47 may consist of 30 wt.% to 70 wt.% recycled long fibre material, 20 wt.% to 60 wt.% recycled short fibre material and 10 wt.% to 50 wt.% broke.

[0101] The top layer 46 may comprise 0,03 wt.% to 0,5 wt.% optical brightening agent as another first component other than water of the top layer 46, based on 100 % total weight of all first components other than water. As examples for suitable optical brightening agents the Tetrasulfo or Disulfo classes of optical brightening agents can be mentioned.

[0102] Furthermore, the top layer 46 may comprise 10 wt.% to 25 wt.% precipitated and / or ground calcium carbonate as another first component other than water of the top layer 46, based on 100 % total weight of all second components other than water.

[0103] The support layer 47 may comprise 15 wt.% to 35 wt.% precipitated and / or ground calcium carbonate as another second component other than water of the support layer 47, based on 100 % total weight of all second components other than water.

[0104] Both the top layer 46 and the support layer 47 may comprise additives commonly used in the art of paper making, such as for example sizing agents, starch or other bulk additives. The top layer 46 may comprise further pigments or dyes as additives, for example for colouration purposes, respectively for production of coloured multi-layer paper liners 45.

[0105] Finally, the top layer 46 of the multi-layer paper liner 45 may have a grammage of 45 g / m 2< to 63 g / m 2< , preferably may have grammage of 45 g / m 2< to 61 g / m 2< and in particular may have grammage of 45 g / m 2< to 57 g / m 2< .

[0106] In the following, some examples are presented to illustrate the high effectiveness in mottling reduction of a dye exhibiting a blackish colour in the top layer 46 of the multi-layer paper liner 45, respectively in the first paper web layer of the uncut multi-layer paper liner web 30.

[0107] All of the examples and comparative examples were produced according to the method described above, wherein for all (comparative) examples the same types and amounts of bleached virgin cellulose fibre material and unbleached cellulose fibre material were used.

[0108] In the following table 1, comparative examples Comp 1 and Comp 2 are given, which had been produced without a dye exhibiting a blackish colour in the top layer, whereas the examples 1 to 4 each had top layers 46 with a content of 0,03 wt. % of dye exhibiting a blackish colour or black dye (Pergasol ™< Black 18 Lna). The grammages of the top layers of the (comparative) examples were: Comp 1: 64,23 g / m 2< Comp 2: 60,77 g / m 2< 1: 53,9 g / m 2< 2: 54,54 g / m 2< 3: 54,21 g / m 2< 4: 54,96 g / m 2<

[0109] Furthermore, in table 1 contents of optical brightness agent (OBA) of the Tetrasulfo class and varying contents of precipitated calcium carbonate (PCC) in the respective top layers are given. The so-called Kheops values were measured with the Kheops equipment / sensor (Techpap) commonly used for characterizing surface quality and optical appearance of paper surfaces in paper technology. As person skilled in the art of paper making know, such Kheops equipment for evaluating mottling essentially comprises a CCD camera and a diffused light sources. As is also known by those skilled in the art, these Kheops values are representative for the degree of mottling, with lower Kheops values designating lower degrees of mottling. Table 1:ExampleBlack dye content (wt.%)OBA content (wt.%)PCC content (wt. %)Kheops valueComp 100,0818,126,14Comp 200,0820,866,1710,030,118,785,3820,030,118,375,3730,030,120,825,2640,030,122,475,15

[0110] From the results resented in table 1 the remarkable efficiency of mottling reduction of the dye exhibiting a blackish colour, or black dye as designated in table 1, can immediately be seen. Even at the low contents depicted in table 1, the dye exhibiting a blackish colour leads to a significant reduction of mottling, as illustrated by comparing the values for the comparative examples with the values of the samples comprising the dye exhibiting a blackish colour in the top layer, which showed a significant drop in the Kheops values. All of the examples 1 to 4 of table 1 had a top layer with a brightness according to ISO 2470 of more than 70 %.

[0111] With the slight variation of the amount of optical brightness agent, the optical appearance, in particular the brightness could be set to a desired value. The variation of the content of optical brightness agent itself however did not cause any significant change regarding the Kheops value, as could be deduced from further, comparative tests.

[0112] Regarding the content of precipitated calcium carbonate in the top layer, higher contents appear to further reduce mottling, wherein slight variations of PCC content per se did not lead to significant changes in mottling. Ground calcium carbonate (GCC) may be used instead of or in conjunction with precipitated calcium carbonate (PCC).

[0113] The embodiments illustrated as examples represent possible variants and it should be pointed out at this stage that the invention is not specifically limited to the variants specifically illustrated, and instead the individual variants may be used in different combinations with one another and these possible variations lie within the reach of the person skilled in this technical field given the disclosed technical teaching.

[0114] The protective scope is defined by the claims. However, reference may be made to the description and drawings with a view to interpreting the claims. Individual features or combinations of features from the different examples of embodiments described and illustrated may also be construed as independent embodiments of the solutions proposed by the invention. The objective underlying the individual solutions proposed by the invention may be found in the description.

[0115] For the sake of good order, finally, it should be pointed out that, in order to provide a clearer understanding of the structure, elements are illustrated to a certain extent out of scale and / or on an enlarged scale and / or on a reduced scale.List of Reference Numbers

[0116] 1First pulp31First paper web layer2Second pulp32Second paper web layer3Stock preparation unit33Forming section4Bleached virgin cellulose fibre material34Hybrid former35Gap former5First pulp preparation line36Press section6Refiner37TriNip press7First mixing chest38Surface processing unit8Additive(s)39Surface treatment substance9First machine chest40Dryer section10First dilution and cleaning unit41Pre-drying section11Water42Post-drying section12Dye43Cylinder13First headbox44Carrier roll14Paper machine45Multi-layer paper liner15Second pulp preparation line46Top layer16Recycled long fibre material47Support layer17Processing device18Recycled short fibre material19Second mixing chest20Broke21Additive(s)22Second machine chest23Second dilution and cleaning unit24Second headbox25First web26Second web27Multi-layer web28First layer29Second layer30Multi-layer paper liner web

Claims

1. Method for producing a multi-layer paper liner web (30), comprising - providing a first pulp (1) consisting of 95 wt.% to 99,9 wt.% water and 0,1 wt.% to 5 wt.% first components other than water, said first components other than water comprising 65 wt.% to 99,99 wt.% bleached virgin cellulose fibre material (4), - providing a second pulp (2) consisting of 95 wt.% to 99,9 wt.% water and 0,1 wt.% to 5 wt.% second component(s) other than water, said second component(s) other than water comprising 65 wt.% to 100 wt.% unbleached cellulose fibre material, - forming a first web (25) out of the first pulp (1) and forming a second web (26) out of the second pulp (2), - joining the first web (25) and the second web (26) to one another, thereby forming a multi-layer web (27) with the first web (25) constituting a first layer (28) and the second web (26) constituting a second layer (29), wherein the first web (25) and the second web (26) are connected to each other, - dewatering and drying the first web (25) and the second web (26) in multiple dewatering / drying steps to form the multi-layer paper liner web (30) having a first paper web layer (31) formed from the dewatered / dried first web (25) and a second paper web layer (32) formed from the dewatered / dried second web (26), the first paper web layer (31) and the second paper web layer (32) being connected with each other, characterized in that as one of the first components other than water of the first pulp (1) a dye exhibiting a blackish colour is added to the first pulp (1).

2. Method according to claim 1, characterized in that the dye exhibiting a blackish colour is added to the first pulp (1) in an amount of 0,01 wt.% to 0,1 wt.% based on 100 % total weight of all first components other than water.

3. Method according to claim 1 or 2, characterized in that as unbleached cellulose fibre material of the second pulp (2) a recycled wastepaper material is used.

4. Method according to any one of the preceding claims, characterized in that as unbleached cellulose fibre material of the second pulp (2) a cellulose fibre material consisting of 30 wt.% to 70 wt.% recycled long fibre material (16), 20 wt.% to 60 wt.% recycled short fibre material (18) and 10 wt.% to 50 wt.% broke is used.

5. Method according to any one of the preceding claims, characterized in that immediately before joining the first web (25) and the second web (26) to one another and forming the multi-layer web (27), a consistency of both the first web (25) and the second web (26) is set to 8 % to 14 % respectively.

6. Method according to any one of the preceding claims, characterized in that, as another first component other than water of the first pulp (1), an optical brightening agent is added to the first pulp (1) in an amount of 0,03 wt.% to 0,5 wt.%, based on 100 % total weight of all first components other than water.

7. Method according to any one of the preceding claims, characterized in that, as another first component other than water of the fist pulp (1), precipitated and / or ground calcium carbonate is added to the first pulp (1) in an amount of 10 wt.% to 25 wt.%, based on 100 % total weight of all first components other than water.

8. Method according to any one of the preceding claims, characterized in that, as another second component other than water of the second pulp (2), precipitated and / or ground calcium carbonate is added to the second pulp (2) in an amount of 15 wt.% to 35 wt.%, based on 100 % total weight of all second components other than water.

9. Method according to anyone of the preceding claims, characterized in that a grammage of the first paper web layer (31) of the multi-layer paper liner web (30) after complete dewatering / drying is set to 45 g / m2 to 63 g / m2.

10. Multi-layer paper liner (45), in particular produced by a method according to any one of claims 1 to 9n, comprising - a top layer (46) consisting of 6 wt.% to 11 wt.% water and 89 wt.% to 94 wt.% first components other than water, said first components other than water comprising 65 wt.% to 99,99 wt.% bleached virgin cellulose fibre material, - a support layer (47) consisting of 6 wt. % to 11 wt.% water and 89 wt.% to 94 wt.% second components other than water, said second component(s) other than water comprising 65 wt.% to 100 wt.% unbleached cellulose fibre material, wherein the top layer (46) and the support layer (47) are connected to each other, characterized in that the top layer (46) comprises a dye exhibiting a blackish colour as one of the first components other than water.

11. Multi-layer paper liner according to claim 10, characterized in that top layer (46) comprises 0,01 wt.% to 0,1 wt.% of the dye exhibiting a blackish colour, based on 100 % total weight of all first components other than water.

12. Multi-layer paper liner according to claim 10 or 11, characterized in that the unbleached cellulose fibre material of the support layer (47) is a recycled wastepaper material.

13. Multi-layer paper liner according to any one of claims 10 to 12, characterized in that the unbleached cellulose fibre material of the support layer (47) consists of 30 wt.% to 70 wt.% recycled long fibre material, 20 wt.% to 60 wt.% recycled short fibre material and 10 wt.% to 50 wt.% broke.

14. Multi-layer paper liner according to any one of claims 10 to 13, characterized in that the top layer (46) comprises 0,03 wt.% to 0,5 wt.% optical brightening agent as another first component other than water of the top layer (46), based on 100 % total weight of all first components other than water.

15. Multi-layer paper liner according to any one of claims 10 to 14, characterized in that the top layer (46) comprises 10 wt.% to 25 wt.% precipitated and / or ground calcium carbonate as another first component other than water of the top layer (46), based on 100 % total weight of all second components other than water.

16. Multi-layer paper liner according to any one of claims 10 to 15, characterized in that the support layer (47) comprises 15 wt.% to 35 wt.% precipitated and / or ground calcium carbonate as another second component other than water of the support layer (47), based on 100 % total weight of all second components other than water.

17. Multi-layer paper liner according to any one of claims 10 to 16, characterized in that the top layer (46) has a grammage of 45 g / m2 to 63 g / m2.

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